The present invention relates generally to a method for painting panels and, in particular, to a method for painting the outer panels of an automobile body.
Typically, rotary type electrostatic spray painting devices, bell atomizers or applicators that generally apply round or elliptical patterns, are used to paint the outer panels of an automobile body as the body is moved along an assembly line. The desired result is a good painted surface of uniform required film thickness. However, the paint application distribution inherent in bell applicators and the shapes of the body panels present many problems to be overcome.
For example, the outer side panels of an automobile body include front and rear wheel openings or cutouts. Thus, portions of these side panels over the wheel openings have a shorter vertical length than other portions. In order to properly paint the shorter portions, one prior art solution is to locate bell applicators above and below a central horizontal plane of the side panels. In this configuration, a distance between the side panel and the spray head is always constant such that a good painted surface is obtained. Since, however, the side panels are divided into two or three portions for painting, four to six spray heads are necessary for one coating. As a result, the painting system requires a large space in which to locate the many spray heads, and the equipment costs are relatively high.
Another prior art electrostatic spray painting device has spray heads that move up and down along a vertical line to enable the outer side panels to be painted by one spray head, so that the number of spray heads needed by the painting device is drastically reduced. However, in this painting device, since the spray head moves away from the side panel during reciprocation of the spray head due to a configuration of the side panel, the electrostatic charge of the paint particles may be lost. In this case paint particles that have lost their electrostatic charge will adhere to the side panel and the quality of the painted surface is degraded.
Another prior art solution is to spray onto the side panels with spray heads moving along an outline of the panels. Such a configuration requires a programmed movable member that maintains the spray head a uniform distance from the side panel surface and aligns an axis of the spray head substantially perpendicular to the adjacent plane of the side panel.
Conventional painting methods use a standard xe2x80x9cWxe2x80x9d (FIG. 1) wave pattern which results in a trapezoidal film build profile (FIG. 2). This pattern is acceptable and desired when meeting additional xe2x80x9cWxe2x80x9d wave patterns at the edges. When painting the edge of a panel the spray pattern must be significantly extended past the edge of the panel to attain acceptable uniformity or a perpendicular stroke is required to add additional film build at the edges. The perpendicular reinforcement stroke is undesirable because it requires additional machine travel and wasted time moving to and from the start and end of the pattern.
The present invention concerns a method for painting a panel using a bell applicator comprising the steps of: providing a bell applicator; providing paint to the applicator; defining a painting pattern with a plurality of points on a surface of a panel to be painted, the pattern extending in a predetermined direction and the points defining opposite edges of the pattern extending in the predetermined direction, at least one edge of the pattern being adjacent an edge of the panel; and moving at least the applicator relative to a panel to apply the paint to the surface of the panel in the predetermined pattern having a desired film thickness, the pattern including a first plurality of pattern segments and a second plurality of reinforcing segments, the pattern segments being connected together each extending between an associated pair of the points on the opposite edges of the pattern, and the reinforcing segments each extending between an associated pair of the points at the at least one edge of the pattern adjacent the edge of the panel. The pattern can include: a xe2x80x9cWxe2x80x9d shaped triangular pattern formed by the pattern segments; a triangular pattern of substantially vertical ones of the pattern segments alternating with angled ones of the pattern segments; a crossing triangular pattern formed by crossed pairs of the pattern segments; or a square pattern having opposed sides formed by pairs of the pattern segments.
The reinforcing segments can include longer reinforcing segments extending in the predetermined direction and shorter reinforcing segments extending transverse to the predetermined direction connecting opposite ends of each of the longer reinforcing segment to the associated pair of points. The method also can include including a third plurality of reinforcing segments each extending in the predetermined direction between an associated pair of the points at another one of the edges of the pattern. A plurality of different painting patterns can be stored and one of the stored patterns selected for performing the method. The pattern segments and the reinforcing segments are applied to the surface of the panel as a continuous pattern including applying the paint continuously to the surface of the panel from a beginning to an end of the pattern.
The invention also concerns a system for painting a panel using a bell applicator including: a bell applicator; a source of paint connected to said bell applicator; and a control means connected to said bell applicator for moving at least said bell applicator relative to a panel to apply paint from said source to a surface of the panel in a predetermined pattern having a desired film thickness, said pattern extending in a predetermined direction and including a plurality of connected segments extending between spaced apart points defining opposite edges of said pattern extending in said predetermined direction, at least one of said segments being a reinforcing segment extending in said predetermined direction between a pair of said points at one of said edges of said pattern adjacent an edge of the panel. The pattern is a selected one of a plurality of painting patterns and the system includes a memory connected to said control means for storing said plurality of painting patterns. The system also includes an input device connected to said control means for selecting one of said plurality of painting patterns.